1. Field of the Invention
This invention concerns a composition containing pigment dispersed in a reaction product of polyamines and polyisocyanates. More particularly, this invention relates to a composition containing at least a pigment dispersed in a dispersing agent, which possesses excellent dispersion stability of the pigment, lower thixotropy and an excellent flow property.
2. Description of the Prior Art
In conventional compositions containing dispersed pigments composed of pigments, resins and solvents, if the dispersibility of the pigment to the resin is poor, the composition containing the dispersed pigment exhibits remarkable thixotropy due to the flocculation of the pigment. Further, since paint films formed by applying a composition containing a dispersed pigment having flocculated pigments cause various problems such as degradation in the gloss, a decrease in the distinctiveness of image, reduction in the color strength, flooding, etc., sufficient performance of the pigment can not be obtained with such compositions containing the dispersed pigment.
In order to overcome the foregoing problems, various inventions have been proposed as described below.
(1) There has been a method of incorporating certain pigment derivatives into pigment as shown in Japanese Patent Laid-Open No. 18736/1976, but this method can not be applied to general use for various pigments since such pigment derivatives are colored by those structures.
(2) There has also been disclosed, for example, in Japanese Patent Laid-Open No. 160396/1975 and British Patent Specification Nos. 1393401 and 1393402 a technique of utilizing, as a dispersing agent, those compounds obtained by reacting three groups of compounds, that is, organic compounds having at least two isocyanate groups, i.e., polyisocyanate (group A), organic compounds having at least two functional groups reactive with the isocyanate groups, for example, amino groups or hydroxyl groups (group B) and polymers (group C) having one functional group reactive with the isocyanate groups. These dispersing agents have, however, the defect as described below.
The design concept for the dispersing agent of this type is to prepare a block structure comprising chains that can be solvated with solvents and polar anchor group portions adsorptive to the pigment as stated by A. Topham in "Progress in Organic Coatings", Vol. 5, (1977), pp 237-243. When employing this technique, it is necessary to prepare a composition containing dispersed pigment comprising the dispersing agent as described above, the solvent and the pigment and, in the case of preparing paints using the composition, it is generally further necessary to add various types of resins as the film forming vehicles. In this case, the type and amount of vehicle resins to be added as the film forming ingredients are restricted in view of the compatibility between the film forming resins and the polymer constituting the dispersing agent. Accordingly, it has been difficult to use such dispersing agents for general purpose application. Particularly, they have insufficient effects on the pigments and poor dispersibility, for example, with quinacridone pigments. Further, problems may occur in the durability or other areas of film performance of the paint films containing a large amount of dispersing agent used for dispersing pigments as described in the prior art and literature. A certain complexity of production steps required to utilize these prior techniques is imposed, such as the requirement for the prior synthesis of the dispersing agent, as well as the prior synthesis of the ingredients, that is, the polymers of the group C, necessary for synthesizing the dispersing agent.
Moreover, the conventional dispersing agents have previously been synthesized and have been used by being blended with pigments and vehicle resins upon dispersing the pigments. Since the conventional dispersing agents have been prepared and used in these ways, when they are used, for example, for the preparation of paints, they produce undesirable effects on the paints and the condition of the paint films due to the restriction caused from the composition of the dispersing agents, such as poor compatibility between the dispersing agents and the vehicle resins, the restrictions on the types of solvents to be used or a reduction in the water resistance of the paint films.